glplatform
==========

`glplatform` provides a framework for developing OpenGL applications without taking control over the application's main loop. It handles window creation, event processing, OpenGL context management, and OpenGL binding management. `glplatform` is designed to make it easy to create an OpenGL application but does not serve as general purpose platform abstraction library. At present GNU/Linux and Windows are supported. Support for other platforms may be added later as variants of the present interface.

Creating a window
-----------------

A window can be created in by calling `glplatform_create_window()` specifying its title, initial dimentions, framebuffer format, and a structure containing event callbacks. If no framebuffer format is specified then a framebuffer 24-bit color buffer and a 24-bit depth buffer will be requested. The event callbacks will be called inside `glplatform_process_events()` (see below).

Example: Create a "Hello world" window

	#include <glplatform/glplatform.h>

	void on_key_down(struct glplatform_win *win, int k)
	{
		printf("Key pressed: %c\n", k);
	}

	int main()
	{
		struct glplatform_win_callbacks cb = {
			.on_key_down = on_key_down
		};

		struct glplatform_win *win = glplatform_create_window("Hello window", &cb, NULL, 512, 512);
		//...
	}

Event processing
----------------

`glplatform` invokes callbacks for previously queued events when `glplatform_process_events()` is called. Events are queued by `glplatform_get_events()`.

Example: A simple main loop

	int main()
	{
		//...
		while (glplatform_process_events()) {
			if (glplatform_get_events(true) < 0)
				break;
		}
	}

If false is passed into `glplatform_get_events()` then `glplatform` will not block and returns the number of events queued, allowing the user to poll for events. On Linux `glplatform` uses `epoll()` to wait for events and it exposes the epoll file descriptor it uses to the application as `glplatform_epoll_fd`. This may allow for `glplatform` event processing to be performed in combination with other event processing systems without polling.

Creating an OpenGL context
--------------------------

When creating a context you must specify which OpenGL version your application requires and the window that the context will be rendering to. The version on the returned context may be higher but will be backwards compatible with the requested version. The returned context will always be a core profile context. Before OpenGL calls can be made the context must be made current with `glplatform_make_current()`. This causes OpenGL commands in the current thread to operate in the context.

Example: Creating a OpenGL 3.3 core profile compatible context

	struct glplatform_win *win = glplatform_create_window("Hello window", &cb, 512, 512);

	//...

	glplatform_gl_context_t ctx = glplatform_create_context(win, 3, 3);
	if (!ctx)
		exit(-1)

	glplatform_make_current(win, ctx);

Function pointer binding
------------------------

Once a context has been made current OpenGL calls cannot be issued until the OpenGL API's function pointers are bound. `glplatform` contains bindings generated by `glbindify` for this purpose.

Example: Initializing OpenGL bindings

	#include <glplatform/glplatform.h>
	#include <glplatform/glplatform-glcore.h>

	int main()
	{
		struct glplatform_win *win;
		glplatform_gl_context_t ctx;

		//...

		glplatform_make_current(win, ctx);

		if (!glplatform_glcore_init(3, 3)) {
			exit(-1);
		}
	}


See the `glbindify` documentation for details. Note that `glplatform` uses the namespace feature of `glbindify` so where the documentation refers to `glb` or `GLB` you should substitute `glplatform` or `GLPLATFORM`
respectively.

Building
--------

On GNU/Linux systems `glplatform` can be built with it's autotools build system.

	./autogen.sh
	./configure <options>
	make
	make install

On Windows systems `glplatform` can be built as a static library using the Visual Studio solution found in the `windows` folder.

As a convienence `glplatform` comes with bindings pre-generated by `glbindify`. To rebuild them install `glbindify` and run the following commands:

	glbindify -a gl -n glplatform
	glbindify -a wgl -n glplatform
	glbindify -a glx -n glplatform

After the files generated copy them into `src/glbindings` and the generated header files into `include/glbindings`.
